Effective and Safe Administration of Low-Dose Estramustine Phosphate for Castration-Resistant Prostate Cancer.

Despite the favorable toxicity profile at the standard dose of 560 mg daily, the tolerability and toxicology of estramustine phosphate (EMP) have been a cause for concern at administration. Moreover, we do not know whether a lower dose of 280 mg of EMP daily can be administered with some efficacy and fewer side effects. The results of our phase II study suggest that low-dose EMP is a safe treatment option with the same efficacy in patients with castration-resistant prostate cancer.

BACKGROUND

We evaluated the efficacy and safety of low-dose estramustine phosphate (EMP) in Japanese patients with castration-resistant prostate cancer (CRPC).

METHODS

The present study was a single-arm, nonrandomized prospective study in which all patients received EMP orally twice daily for a total dose of 280 mg/day. A total of 31 patients with CRPC were enrolled from December 2009 to December 2012 at 5 institutions in Japan. The primary endpoint was the prostate-specific antigen (PSA) response, defined as a 50% decline in the serum PSA level, confirmed ≥ 3 weeks later. The secondary endpoints included the objective response rate, interval to PSA progression, PSA response duration, progression-free survival, disease-specific survival, overall survival, safety, and quality-of-life assessment using the Functional Assessment of Cancer Therapy-Prostate scores.

RESULTS

Ten patients (32%) had a PSA response, and no patient had an objective response. The treatment was well tolerated, and the most frequent toxicities were grade 1 to 2 nausea/vomiting, anorexia, and gynecomastia. The median interval to PSA progression was 140 days (95% confidence interval [CI], 117-260 days). The PSA response duration was 119 days (95% CI, 49-219 days). The median progression-free survival was 213 days (95% CI, 167-422 days). The 3-year disease-specific survival and overall survival rates were 68.6% (median not reached; 95% CI, 33 months to not available) and 59.9% (median 42 months, 95% CI, 28 months to not available), respectively.

CONCLUSIONS

Low-dose EMP seems to be a safe treatment option with some efficacy in patients with CRPC.